Tanker trucks are commonly used for storing or transporting volatile or flammable materials, such as gasoline, diesel fuel or other petroleum products, which materials often produce large quantities of hazardous and toxic vapors that can pollute the environment. In order to preserve the quality of the atmosphere, such trucks are typically constructed with one or more sealed tanks that retain the vapors and prevent their escape. The sealed tanks are effective in retaining the vapors, but over time, the tanks can develop leaks that allow the vapors to escape.
In order to insure that the truck tanks are vapor "tight", by regulation, each of the tanks on a truck must be periodically subjected to inspections and tests and certified as vapor tight and leak-free. Such a certification is valid for a predetermined period of time, after which the certification expires, and the truck must be re-inspected. Recently, more stringent laws have been passed which require the vapor tightness certification of each truck to be checked and verified as valid each time the truck is to be filled and before filling actually commences.
One way of accomplishing this mandated verification is to track the certification manually. With this method, a plaque or identification (ID) label is permanently mounted on the truck, which ID label contains a serial number which is unique to the truck. Prior to a filling or loading operation, the serial number is observed by loading personnel and manually compared against a list of serial numbers assigned to trucks that have active or valid certifications. With such a manual system, a paper audit trail must be kept on each truck to verify that its certification has, in fact, been checked and verified prior to each loading.
While such a manual system is suitable for a very small operation involving only a few trucks and loading terminals, it involves a significant amount of paperwork to keep track of the truck certification data and quickly becomes cumbersome and inordinately time-consuming in large systems involving many trucks and busy loading terminals.
In an attempt to automate the verification process, some trucks have been fitted with special radio-frequency (RF) transponder plates. These plates respond to an RF signal generated by a transmitter located at the loading terminal and generate a low-power ID signal. This ID signal is detected and then used to identify the truck. A computer system uses the truck ID to retrieve information regarding the truck vapor tightness certification. The computer system uses the information to verify that the certification is valid before loading is allowed.
In some circumstances, these RF transponder systems work well, but the RF transmitter is relatively expensive. Further, the placement of the RF transponder plate on the vehicle is critical to produce a satisfactory response. Due to the expense and the placement difficulties, the RF transponder system is not widely used.
It is also possible to place a small memory on board the tanker truck which memory can store information about the truck, including a unique identifying number and other truck information. However, it is difficult to read the information from the memory using available equipment. More particularly, tanker trucks are typically filled by pumping equipment located at a loading rack or terminal. In order to prevent the truck tanks from overflowing doing the loading process, an overfill protection device is commonly used with each tank mounted on the truck to automatically disable the pumping equipment when the tank capacity limit has been reached. In addition, since the tanker trucks often carry flammable cargo, it is necessary to insure that the truck is properly grounded during the loading process so that no spark or electrical discharge will ignite the flammable or hazardous vapors that are created and this is typically done by using an automated ground proving system.
Overfill protection devices which are commonly on the market have a probe located within each tank that generates a fluctuating electrical signal when the fluid within the tank is less than a predetermined level. The probe is connected to an overfill circuit which is typically located on the loading terminal by an electrical cable which passes between the truck and the loading terminal. When the fluctuations in the probe signal cease, indicating a particular tank on the truck is filled, the overfill circuit operates to stop liquid flow into that tank by disabling the pumping equipment at the loading terminal. Such an overfill system and the probe used therewith is described in more detail in copending U.S. patent application, Ser. No. 08/076,809 entitled "Fail Safe Fluid Level Detection Circuit" filed on Jun. 14, 1993 by Arthur W. Shea and assigned to the same assignee as the present invention. The disclosure of the latter application is hereby incorporated by reference. Conventional ground proving systems also use the existing cable between the loading terminal and the tanker truck to carry electrical signals that verify the existence of a proper ground.
In order to use an on-board memory for vapor tightness certificate verification, it would be convenient to utilize the existing overfill/grounding system electrical cable to also transmit information to an on-board memory and receive information from the memory. However, in practice, this is difficult to do, because although the existing cable has multiple conductors, in many situations, all of the conductors are assigned to overfill or grounding signals and there are no free conductors. The cable may be relatively easily replaced in order to add additional conductors, but the connectors at the ends of the cable are not easily replaced and thus, the number of conductors is effectively fixed. Sharing of one or more conductors is possible, but the signals presently on the conductors are often inhospitable to the signals necessary for operation of an on-board memory.
For example, in order to make both the overfill protection system and the ground proving system "fail safe", it is common practice to use special signal arrangements on these circuits to prevent tampering and overriding of the circuits by placing shorts across the wiring. A common method of operating a ground proving system is to place a small alternating current signal on the ground lead which connects the truck to the loading terminal. At the truck end, the ground lead is connected to a ground bolt located on the truck which effectively connects the truck to the terminal and grounds the truck. The ground bolt contains a diode that rectifies the small alternating current signal and the rectified signal is sensed by a detection circuit at the loading terminal to verify that the vehicle has been properly grounded. The use of an alternating current signal guarantees that simply placing a short across the grounding wire in the cable that connects the loading terminal to the vehicle will not produce an indication that the truck is properly grounded. Such a grounding system is, for example, sold by the assignee of the present invention under the tradename "GROUNDHOG.RTM." and is described in detail in U.S. Pat. No. 4,901,195, which patent is hereby incorporated by reference.
As described above, a similar fluctuating signal arrangement is used in existing overfill protection systems in order to prevent a simple short circuit or open circuit from erroneously masking an overfill situation. The presence of these fluctuating signals prevents proper operation and use of a conventional memory on board the truck. In the case of the aforementioned grounding system, the fluctuating signal may have an amplitude of between 10-50 volts and so the signal itself can damage conventional memory circuitry that generally has a maximum voltage rating of five volts.
Accordingly, it is an object of the present invention to provide a vehicle identification and verification system which can positively identify a vehicle.
It is another object of the present invention to provide a vehicle identification and verification system which can utilize an on board memory to store vehicle information, including unique identifying numbers, dates or other verification information.
It is still another object of the present invention to utilize existing overfill/grounding system cable connections between a loading terminal and a vehicle in order to identify the vehicle and retrieve information from the vehicle.